The present invention relates to a method of operating a spark ignition internal combustion engine having fuel injection at a cold start.
To start a spark ignition internal combustion engine having direct fuel injection, an initial pressure of, for example, about 4 bar, may be created using an electrical fuel pump. The fuel injection may be limited by an angle window, the beginning of which may be defined by the moment of opening of an inlet valve and the end of which may be determined by the combustion chamber pressure established in the cylinder. Since the pressure in the combustion chamber rises during a compression phase and exceeds the initial pressure created by the electrical fuel pump starting at a certain piston position, the fuel injection should end when the pressure in the combustion chamber exceeds a certain pressure threshold. Otherwise, air may be blown from the combustion chamber into the inlet valve, which may cause this air, instead of fuel, to be injected through the inlet valve into the combustion chamber during a subsequent injection. This may disadvantageously cause combustion misfiring in the corresponding cylinders.
Consequently, the beginning and the end of a fuel injection, which is limited by an angle window, are determined by a certain rotational angle position of the crankshaft, the respective rotational angle positions at the beginning and end of the injection enclosing a corresponding variable angle of rotation of the crankshaft. The time interval during which the crankshaft passes through this angle of rotation is proportional to the rotational speed of the engine.
When the internal combustion engine is cold-started, very long injection times may be required, at least for initial combustions. When the fuel injection times are long, the fuel reaching the combustion chamber from the first two injections may combust and cause a significant increase in rotational speed. Due to the increase in rotational speed, there may not be sufficient injection time available for the subsequent third and fourth injections to inject an adequate quantity of fuel for combustion into the combustion chamber using the inlet valve (injection valve). This may cause unwanted combustion misfirings during the third and fourth injections at cold start.
To avoid these unwanted combustion misfirings during the cold start, an additional injector (cold start injector), which may be positioned in the intake pipe of the engine, injects additional fuel into the injection chamber simultaneously with the intake valve during the cold start. However, it is believed that such an additional cold start valve may be relatively complicated and costly.
An exemplary method according to the present invention for operating a spark ignition internal combustion engine having fuel injection at a cold start includes the following steps:
retarding the spark angle to a cold start value for at least the first combustion in at least one cylinder of the internal combustion engine during a cold start phase, while the fuel injected into the cylinder is brought to combustion; and
setting the spark angle to normal to end the cold start phase.
Since the spark angle is retarded as much as possible for at least the first combustion in at least one cylinder, the fuel or fuel-air mixture injected into the combustion chamber is burned up in the corresponding ignition, and as such, a small torque is produced by this combustion.
Consequently, the first combustion, using a retarded spark angle, results in a slight increase in rotational speed, so that there may be sufficient injection time available for the next injection to inject sufficient fuel into the combustion chamber, so that reliable combustion may be ensured, or at least made more probable. Further, since the combustion chamber warms up after the first combustion, less fuel may be injected into the combustion chamber to ensure a next combustion. Thus, a retarding of the spark angle for at least the first combustion in each respective cylinder during a cold start results in warming of the combustion chamber, while the increase in rotational speed of the engine is reduced. In this manner, successful combustion for the next injection is ensured, or at least made more probable, since less injected fuel may be required for the following combustion, due to the warming of the combustion chamber by the first combustion, while at the same time more injection time may be available for injecting fuel into the (warmed) combustion chamber due to the relatively slight increase in rotational speed. Thus, combustion misfirings during cold start may be prevented, or at least reduced, in a simple and reliable way.
The cold start phase may include a plurality of combustions. Due to the low increase in rotational speed during the first combustions with a late spark angle, the retardation of the spark angle is not limited to the first combustion during the cold start, but may be extended to a desired optimal number of combustions to achieve effective warming of the combustion chamber and to optimize additional cold start parameters.
The spark angle is reset to normal in a single step, to set a desired operating performance value. This permits a quick change from retarded spark angles to appropriate normal spark angles after the cold start phase ends, at which an elevated or maximum possible spark angle operating efficiency may be achieved.
The spark angle is reset to normal in a plurality of transitional steps, to set a desired operating performance value. To avoid too great a change in the spark angle, the reset to normal, which ends the cold start phase, may occur in several transitional steps, until the desired normal spark angle is set to utilize maximum possible spark angle operating efficiency.
According to an exemplary embodiment of the present invention, the cold start value is individually set for each cylinder. Since the cold starting response of the various cylinders of an internal combustion engine may differ, a cold start value for each individual cylinder may be calculated and set, to ensure effective prevention of combustion misfirings, while at the same time maintaining the maximum possible spark angle efficiency.
The cold start value may be set during the cold start phase for the next combustion of each corresponding cylinder. Since increased warming of the combustion chamber is achieved during the cold start phase with each combustion, a specific cold start value for each individual cylinder for each individual combustion may be calculated and set. In this manner, the retardation of the spark angle during the cold start phase is kept as small as possible, so that an optimized spark angle operating efficiency may be attained, even during the cold start phase.
The cold start value is set using a retardation setting that is adapted to the operating temperature of a particular cylinder. In this manner, the cold start value of the spark angle may be kept at the lowest level possible, to achieve optimal spark angle operating efficiency, while reliably preventing combustion misfirings during the cold start phase.
The spark angle is retarded if the number of ignitions is smaller than or equal to the value of a parameter, which is greater than or equal to one and less than or equal to the number of cylinders in the engine, and the combustion chamber temperature before the first ignition is lower than a threshold temperature. This permits the retardation during the cold start phase to be limited to a defined number of ignitions, for example, alternative polling. The combustion chamber temperature before the first ignition may be at least approximately determined from the coolant temperature, the oil temperature and/or the intake air temperature of the engine. The temperature threshold may be, for example, approximately 0xc2x0 C.